In addition to vitamins, minerals, fibers and energy giving nutrients like sugar, carbohydrates, lipids and proteins, fruits and vegetables contain bioactive phenolic and polyphenolic compounds which are not energy giving nutrients, but which are believed to have beneficial physiological and cellular roles, and modify risk of chronic diseases. Consumed over an extended period as a part of a regular diet, these naturally occurring bioactive phenolic and polyphenolic plant constituents can confer a wide range of physiological benefits as natural antioxidants, antiallergic, anticarcinogenic, antiinflammatory, etc.
The phenolic and polyphenolic compounds of dietary significance are polycyclic structures consisting of 15 carbon atoms based on C6-C3-C6 skeleton, and include:
a) Flavonols (e.g. quercetin in apples, cherries)
b) Flavones (e.g. apigenin in celery)
c) Flavan-3-ols (e.g. proanthocyanidin A or PAC in cranberries having antiadhesion role)
d) Flavanones (e.g. naringenin in citrus),
e) Anthocyanins (color pigments of fruits, vegetables and flowers)
f) Isoflavones (present in soy products)
The non-flavonoid polyphenolic compounds having dietary significance include:
a) The C6-C1 Phenolic acids (e.g. gallic acid, ellagic acid in raspberries)
b) The C6-C3 Hydroxy cinnamates (e.g. chlorogenic acid in cherries)
c) The C6-C2-C3 Stilbene (e.g. resveratrol in red wine, pterostilbene in blueberries)
In nature phenolic compounds are commonly found conjugated to sugars and organic acids, and have antioxidant properties as determined by their oxygen Radical Absorbance Capacity (ORAC). The in vitro ORAC test was developed as a relative measure of antioxidant capacity. Fruits and vegetables products rich in health promoting constituents have many benefits and uses including as dietary supplements.
The essentially water soluble anthocyanins are a significant component of some fruits, vegetables and flowers, and bestow them with their red, blue and purple colors. The known anthocyanins exist as the glucosides of polyhydroxy and/or polymethoxy derivatives of the flavylium cation like, cyanidin (red color), pelargonidin (orange-red), peonidin (red-rose), delphinidin (blue-violet), petunidin (blue-purple) and malvidin (purple). Anthocyanins in red tart cherries have been suggested to benefit people suffering from joint pain and inflammation because of their potential role in inhibiting cyclooxygenase enzymes (Cox-1 and Cox-2) which are reported to catalyze the conversion of arachidonic acid to prostaglandins (PGs) which contribute to pathogenesis of inflammation. In rheumatoid arthritis and other inflammatory joint diseases, high concentration of PGs has been detected.
The molecular weight of these bioactive phenolic compounds can range from about 300 to about 700 Daltons. Sugars such as glucose and fructose (C6H12O6) which are the predominant components of fruit juices have molecular weight of 180 Dalton; the fruit juices also contain a small amount of sucrose (C12H22O11) having a molecular weight of 342 Dalton. The organic acids (such as citric acid, C6H8O7; malic acid C4H6O5, tartaric acid, C4H6O6, quinic acid, C7H12O6) in fruits juices can range in molecular weight from 134 to 192 Dalton. Resin separators and high pressure liquid chromatography have been used, but these are chemical processes and often not as economically viable for commercial scale up in separation of bioactive flavanoids from the sugars and food acids of the juices.